Standard terminology in the battery industry will be used to describe battery construction. A cell is a single unit of a battery with a known potential based upon the chemistry of the cell. A number of cells in series is a battery. Primary type batteries convert chemical potential energy into electric current and are not ordinarily rechargeable. Alkaline batteries and carbon-zinc batteries are examples of primary batteries.
Secondary batteries are rechargeable. Typical types of secondary batteries are nickel cadmium, nickel metal hydride, lithium ion and the ubiquitous lead-acid type. Small, portable fuel cells that convert hydrocarbon fuel into electric power will also be considered as primary batteries, although they can be refilled and reused like secondary batteries. Such fuel cells may be used in the future in portable electronic devices, such as cell phones and laptop computers.
The term “mains power” will be used to describe any source of electrical power that is continuously available and is not generally exhaustible by a tool or appliance. Some examples of mains power include the standard 115 VAC, 60 Hz power from wall receptacles found in every home and office, the 12 VDC to 13.8 VDC power available from the cigarette lighter socket found on an automobile dashboard, and the 12 VDC supplied by a domestic solar photovoltaic array. Mains power is typically much less costly than use of primary or secondary batteries for the same amount of power supplied. Of course, batteries have the advantage of portability over mains power.
Tools and appliances that operate solely off of mains power are outside the scope of the present invention. The present invention is concerned with portable or cordless devices which use an on-board source of electrical power. On the less expensive end are devices which operate using primary batteries. Once the battery, or set of cells, is exhausted, it must be replaced at some cost. This may be acceptable for tools which are used intermittently and/or used infrequently since the tool may remain in a high state of readiness for years. Initial cost may also be lower since primary batteries are much less costly than secondary batteries for the same power output.
For tools and appliances which must be used frequently, and which cannot be practically connected to mains power, rechargeable (secondary) batteries are a viable option. Batteries of many cells with voltages of up to 36 VDC for portable tools can be recharged in hours. A construction worker may take a couple of batteries on site and work for hours without needing a connection to the mains power. The much higher cost of the rechargeable batteries can be amortized over hundreds of charges.
The cost of the rechargeable batteries can also be kept down if the same battery can be used with many different tools, such as a drill motor, a jigsaw, a flashlight, a sander, or the like. A battery can be “borrowed” from an infrequently used tool and be placed on a tool which is more frequently used, such as a drill motor, or a tool which draws more power and exhausts the battery more quickly, such as a circular saw.
Secondary batteries tend to self-discharge over time. Thus, they may not be the best choice for standby or intermittent use unless they have a continuous source of charging current to keep them fully charged. Typically, designs of the rechargeable battery packs are proprietary to the tool manufacturer. Thus, they are not interchangeable between manufacturers, or even between different lines of tools from the same manufacturer. If an older battery pack design is no longer offered for sale, the tools which utilize that pack can no longer be used after the existing rechargeable batteries have exceeded their normal life. Adapters to accommodate new style battery packs can be used in only isolated instances and only if the new battery packs supplies the same voltage as the tool uses.
Newer rechargeable batteries typically use non-toxic materials in their construction and are more eco-friendly than primary cells, which take up the same volume but which are disposed of hundreds of times more often. In fact, most types of rechargeable batteries are recycled to reclaim their metallic content.
Rechargeable cells are made to fit the same form factor as standard primary cells (size AAA, AA, C, D, and the like), but rechargeable cells do not typically store as much energy or have as high a voltage. For example a typical voltage for a rechargeable cell is about 1.2 VDC as compared to about 1.5 VDC for a primary cell. Therefore, typical secondary batteries must include more cells than primary batteries to obtain equivalent voltage outputs.
Battery capacity is measured in milliamp-hours. This is the output of the battery (in milliamps] integrated over time (until exhaustion) with the current draw at a specified rate. Higher capacity is usually better. The expression “C” is used to refer to a standard rate of charging and discharging a secondary battery and is determined by dividing the milliamp-hours by hours. Typical charging rates are between 0.1 C and 0.5 C. A very low charge rate is called a “trickle” charge. A trickle charge is typically used to overcome the tendency of a secondary battery to self-discharge.
Lead acid storage batteries, as commonly used in automobiles, have a large current capacity and can be used to generate AC power from its DC output by using a circuit known as an inverter. Among this type of batteries, there are starting batteries, which are good for short bursts of high current, and deep cycle batteries, which are intended to be discharged almost completely and then recharged for many cycles. Starting batteries tend to rapidly deteriorate if used in deep cycle applications.
Battery packs for rechargeable tools and appliances can be found in a wide range of voltages. Some appliances take two battery packs of the same type. It is not common for an appliance to be able to use battery packs of different voltages or different styles. However, it is common for a single battery charger station (operating off of mains power) to accept batteries of different voltages or different mechanical styles. It is not common for an appliance to use both primary and secondary batteries in the same appliance, although some electronic devices have a small primary cell to act as a backup battery for a clock or for a configuration memory. This primary cell does not provide the same function as the rechargeable battery nor does it interoperate with the rechargeable battery.
There are numerous methods of recharging secondary batteries. A major concern is to not overcharge the batteries since this will damage them internally, and reduce their current capacity. One recharging method is to monitor the temperature rise of the cells, since the internal temperature rises rapidly as full charge is approached. Another method is to monitor the charging voltage if the charging current is fixed. The charging voltage will plateau as the charging is completed. Simple chargers assume that the battery is fully discharged and supply a charging current to the battery for a fixed amount of time. Special integrated circuits (ICs) have been developed which supervise the automatic safe charging of batteries. These ICs provide output control signals when charging is complete and they can be programmed to work with different numbers of cells and different cell chemistries.
While battery operation of tools is usually very safe for the user, there is a particular hazard involved in use of removable cells or battery packs. If a number of cells in series connection have one cell reversed in polarity (installed backward), the other cells act to reverse charge the errant cell. This can damage a rechargeable battery permanently and also cause primary batteries to heat up and even leak a caustic electrolyte. A related hazard is use of both old and new batteries in the same series. Older batteries act as a drag on the fresher ones, wasting power. Similar effects are seen if different types of batteries are mixed in a series. Typically, mechanical interlocks are used to prevent reverse installation or to keep the circuit open in the case of incorrect installation of cells.
Most motor driven appliances operate at more than one speed. To achieve this speed control, many techniques and types of circuits are used. In the DC motor realm, low end speed control is achieved with a rheostat or adjustable resistor in series with the motor. Energy is dissipated in the resistor and the motor sees a lower voltage, thus slowing the motor. For lower power motors, a linear voltage regulator circuit may be used to adjust voltage applied to the motor terminals. More efficient motor controls use pulse width modulation (PWM) or pulse frequency modulation (PFM) techniques to provide adjustable (time averaged) voltages to a brush-type DC motor or to a brushless DC motor.
The current controller switches between ON and OFF conditions very quickly so that little energy is dissipated in the switch. Ideally, no current is conducted in the OFF state and no voltage drop occurs in the ON state. A capacitor on the output of the switch smoothes the voltage out so that the motor appears to see a near-DC voltage at some fraction of the supply voltage. The duty cycle of the switch determines the fraction of supply voltage that is output. This type of method can only reduce the voltage (and the power level) below that of the supply voltage.
Another kind of voltage control found in DC-DC power supplies uses inductors in the switching circuit to provide voltages higher or lower than the supply voltage. Some of the circuit topologies are known as flyback, SEPIC, and Cuk. They are still limited to power outputs lower than the power output of the supply voltage, as from a primary or secondary battery. They do, however, allow a circuit to use battery power at one voltage and provide another voltage and, further, to keep that voltage constant until the battery is exhausted, that is, until the power needed exceeds the maximum power that can be supplied.
In the art, there are numerous instances of electric fans which operate from mains power (AC), from DC mains (especially for automotive use) and from primary batteries. Fans powered from primary batteries may use secondary batteries of the same size but lower voltage. However, performance of the fan will not be as good due to the lower voltage. There are also instances of fans which use rechargeable batteries that are charged from the AC mains, such as the Circulair® Model 8020 aromatherapy diffuser. Some DC fans, such as the o2-cool® Model 1054 fan, can also operate off of the mains power using either an adapter for the automotive cigarette lighter socket, or a wall mount power unit in the case of AC mains.
Similarly, in the realm of portable motorized tools, such as drill motors, circular saws, sanders, or the like, such tools are typically operated from AC mains or from rechargeable battery packs. Some tools have the batteries built-in so that some external source of charging current must be supplied, such as at a socket or at a mating connector. Tools using rechargeable batteries are not intended to be operated directly off of the charging current because the charging current is typically much lower than the operating current required by the tool.
Another relevant type of product in the art is the power station. The power station is an enhanced battery charger/battery combination that can charge batteries, provide booster power from on-board secondary batteries and often house other kinds of battery operated devices such as radios, lanterns or the like. Examples include the Black and Decker® Storm Station and the Bosch® Power Box.
It should also be pointed out that the range of tools and appliances which are operated from rechargeable battery packs is increasing. For example, Black and Decker offers a charging station incorporating a radio. The radio can operate from the battery when mains power is off or interrupted. Ryobi has a 10″ fan that only operates from an 18 VDC battery pack. The same battery pack operates many other different power tools which are included in the Ryobi® line.
The overall problem with selecting a portable fan, tool or appliance is to balance the needs for economy, portability and readiness, which are addressed differently by different power sources. Primary batteries are costly on a dollar per hour of operation basis, but have high readiness and portability. Rechargeable batteries are less costly over the life of the product and are almost as portable, However, rechargeable batteries suffer from so-so readiness. The user must constantly maintain the rechargeable batteries in a ready, or fully-charged, state for optimum performance.
Mains operation has average readiness and the best economy, but poor portability. Mains may be down in emergencies, such as storms and heat waves, or may not be found in remote areas.
If it is decided to utilize rechargeable batteries, the problem arises of having multiple incompatible tools/appliances and battery packs. For example, a Black and Decker® battery pack is incompatible with a Makita® saw, and neither manufacturer's battery pack works in a Ryobi® cordless sander. Even older packs from the same manufacturer do not work in newer, higher voltage tools, and vice versa. Readiness suffers because the user has battery packs or tools which cannot be used, or economy suffers because the user has to buy multiple battery packs and chargers to keep a given tool or appliance in a state of readiness for a full day of work between recharge cycles.
Another problem is that the more powerful cordless, especially rechargeable, motorized appliances require correspondingly heavier and bulkier battery packs. This extra weight makes them less portable and more susceptible to damage from dropping. Increased muscle strain and fatigue are encountered by the user due to the extra weight. Accuracy and productivity therefore suffer.
Another problem with the use of primary batteries is that the power output of the batteries is not constant over the lifetime of the battery. In certain applications, the power or speed needs to be constant for a tool to operate at peak effectiveness. Further, a substantial fraction of the original power of the battery remains even when the output voltage is too low to operate the tool. This residual power is discarded when the primary battery is discarded. This is not economical. Because of the low current output of partially depleted primary batteries (and other sources such as photovoltaic panels, fuel cells, or the like), the depleted power source is not capable of directly powering most motorized tools/appliances.
As previously noted, appliances with multiple, replaceable cells can be damaged if the user inadvertently reverses the polarity of one of the cells.
Therefore, there is a need for improved means of providing power for portable motorized tools, fans, appliances and the like that make the best use of primary batteries, secondary batteries and mains power in an economical fashion. There is also a need for improved means of increasing the readiness of the appliance and to extend the usable battery life. Another need is for improved means of having battery packs interoperate with different tools and appliances. There is also a need for improved means of effectively using low current sources such as solar cells and depleted primary batteries to operate power tools and fans. There is also a need for improved means of making portable tools lighter and easier to use for longer periods of time between charging and/or battery pack replacement.
A general object of the present invention is to therefore provide an improved multiple power source control for electrically powered portable motorized tools and appliances such as fans, power sprayers, and drill motors, to permit them to use a wider variety of power sources in an optimal fashion.
Another object of the present invention is to provide a means of interconnecting the various power sources to the motor and to provide control of the interconnects to the various power sources.
A further object of the present invention is to enhance the utility of existing tools and appliances with additional power supply options.
Yet another object of the present invention is to allow the user to keep using the appliance and/or tool for as long as possible away from mains power or without having to purchase fresh cells.
A still further object of the present invention is to provide improved means of effectively using low current sources such as solar cells and depleted primary batteries to operate power tools and fans.